We previously demonstrated that the iron concentration in the globus pallidus and substantia nigra (measured with spectrophotometry) fluctuates during the estrous cycle and pregnancy. Peak concentrations occur at the same time as the sex hormones estrogen, progesterone, prolactin, and luteinizing hormone-releasing are at highest serum levels. In addition, we have shown that the introduction of an iron chelator, desferal mesylate, into the third ventricle interrupts estrous cyclicity. These studies link brain iron to neuroendocrine regulatory mechanisms. The present three-part study is designed to learn: (1) whether the fluctuations in iron during the estrous cycle occur in all or in only select iron-concentrating brain sites as determined by the combined use of the diamino benzidine intensified Perls' reaction for ferric iron and densitometry; (2) whether several sequential pregnancies deplete brain iron stores as determined with both spectrophotometric and histochemical methods; and, (3) if induced changes in caudate-putamen neurotransmitter metabolism affect the accumulation of iron in the globus pallidus and substantia nigra, which receive striatal input. The results suggest that the accumulation of iron in specific brain areas is due to the association of iron with neurotransmitter metabolism.